In general, an image forming device is configured to: irradiate an electrically charged photosensitive drum with a light to change the potential of the irradiated portion on the photosensitive drum to thereby form an electrostatic latent image on the photosensitive drum; supply the electrostatic latent image with a developer to form a developer image; and transfer the developer image onto a recording sheet, whereby a predetermined image is formed on the recording sheet.
As such an image forming device, there is known one having an LED head for emitting a light which is swingably supported by the device body through an arm and a process cartridge provided with a photosensitive drum which is detachably attached to the device body (Refer to Japanese Patent Application Publication No. 5-249767). In this image forming device, when a cover is closed after attachment of the process cartridge, the arm is swung by a mechanism that is activated by being brought into contact with a part of the cover, causing the LED head to come close to a photosensitive drum provided in the process cartridge for positioning. That is, after the position of the process cartridge with respect to the device body has been set, the position of the LED head with respect to the process cartridge is determined. Note that the positioning of the LED head and process cartridge is achieved by an engagement between a positioning hole formed on the LED head side and a projection formed on the process cartridge side.
However, according to a conventional technique, the position of the LED head is determined with respect to the process cartridge, so that the positioning accuracy of the LED head with respect to the device body may deteriorate due to influence of a positioning error between the device body and process cartridge and positioning error between the process cartridge and LED head. When the positioning accuracy of the LED head with respect to the device body deteriorates as described above, the positioning accuracy between a recording sheet which is fed while being positioned with respect to the device body and LED head correspondingly deteriorates, the printing position may shift.